A compressor is an important component of a heating, ventilation, and air conditioning (HVAC) system. In most residential HVAC installations, the compressor is the highest cost component. When an HVAC system fails to operate properly, a service technician is generally called to diagnose and repair the system. When the service technician finds an inoperative compressor, the technician must determine whether the problem is in the compressor, or elsewhere in the HVAC system, including whether the compressor has overheated and simply needs time to cool and reset itself because of some other system fault. Under pressure to make a quick diagnosis and repair, technicians finding an inoperative compressor often replace the compressor with a known “good” compressor, most typically a new one. Historically up to 40% of returned compressors turn out to be good, with no defect found. These incorrect diagnoses translate directly to increased HVAC down time, wasted repair time, labor, and unnecessary labor and parts costs.
Most hermetically sealed compressors include internal protection switch contacts that open the internal compressor motor electrical circuit following a overheat condition as can be caused by a high mechanical load, an anomalously high line voltage, or by excessive compressor cycling. Once the abnormal condition that caused the overheat condition is cleared, most systems recover automatically after the compressor cools to a sufficiently low temperature where the protection contacts close.
Unfortunately, there is no immediate way for a servicing technician to determine if the internal protection contacts of the compressor are closed or momentarily open due to a non-catastrophic overload. The problem is that there is no convenient and more “fool-proof” method for a service technician to determine the state of the protection contacts inside of a sealed compressor at the external compressor electrical circuit terminals. Therefore, what is needed is a non-intrusive electronic control to inform the technician of the open or closed state of the protection contacts.